The present invention relates generally to vehicles such as lawn and garden tractors and more specifically to an interlock system with an operator presence detection switch, wherein a limited portion of the drive system is operable under certain conditions when the operator is away from the vehicle seat.
Lawn and garden tractors and similar vehicles typically include components driven from a power takeoff (PTO) shaft. Many employ a seat switch to sense the presence of an operator and to automatically kill the engine, when the PTO is engaged or under certain other conditions, if the operator leaves his seat. Other condition responsive devices are usually included in the vehicle for such functions as preventing starting or starter cranking if a transmission or PTO is engaged or if a brake is not engaged. An interlock often is provided for permitting PTO engagement only after a PTO switch is operated following a power up, regardless of the initial PTO switch position on power up.
One problem with use of interlock circuits has been the accommodation of optional features on some models of machines without a substantial redesign or increase in cost of the basic circuitry and without interference with any of the desired interlock operations. For example, some vehicles are offered with both a front and a rear PTO while others have only one PTO. The vehicles offered with two PTO shafts often require that one PTO be operable when the vehicle seat is unoccupied; the single PTO vehicles usually prevent PTO operation in the absence of an operator at the seat. Providing desired interlock function operations for both the base model vehicle with one PTO and the vehicle with the optional second PTO has heretofore required completely different interlock circuits, a special and more expensive seat switch, or other costly modifications to the basic interlock circuitry.